# Dynamic Memory Management

The Library makes use of a dynamic memory manager which handles allocation and deallocation of dynamic memory. The methods used for allocation and deallocation are wrapper functions around the native `malloc`, `calloc`, `realloc`, and `free` methods. Hence, the functionality of teh module is very similar to the native C interface but it allows for structured error recovery and application termination in case of failure. It covers especially the following three situations:

- Handling of allocation and deallocation of dynamic memory
- Recovering from temporary lack of available memory
- Panic handling in case a new allocation fails

## Memory Freer Functions

The dynamic memory freer functions are typically functions that are capable of freeing large chunks of memory. In case a new allocation fails, the allocation method looks for any freer functions to call. There can be multriple freer functions and after each call, the allocation method tries again to allocate the desired amount of dynamic memory. The freer functions are called in reverse order meaning that the last one registered gets called first. That way, it is easy to add temporary free functions which then are guaranteed to be called first if a methods fails.

### Add a Freer Function

You can add a freer function by using the following method. The Library itself registeres a set of free functions during initialization. If the application does not register any freer functions then the Library looks how it can free internal memory.

    typedef void HTMemoryCallback(size_t size);

    extern BOOL HTMemoryCall_add (HTMemoryCallback * cbf);

### Delete a Freer Function

Freer functions can be deleted at any time in which case they are not called anymore.

    extern BOOL HTMemoryCall_delete (HTMemoryCallback * cbf);
    extern BOOL HTMemoryCall_deleteAll (void);

## Panic Handling

If the freer functions are not capable of deallocation enough memory then the application must have an organized way of closing down. This is done using the panic handler. In the libwww, each allocation is tested and HT_OUTOFMEM is called if a NULL was returned. HT_OUTOFMEM is a macro which calls HTMemory_outofmem. This function calls an exit function defined by the app in a call to HTMemory_setExit. If the app has not defined this function, HTMemory_outofmem TTYPrints the error message and calls exit(1).

    typedef void HTMemoryExitCallback(char * name, char * file, unsigned long line);

    extern void HTMemory_setExit(HTMemoryExitCallback * pExit);

    extern HTMemoryExitCallback * HTMemory_exit(void);